This invention relates to semiconductor lasers and more particularly to the fabrication of gain-guided semiconductor injection lasers made from II/VI materials and operating in the blue, green and blue-green regions.
Semiconductor lasers made from of III/V materials and operating in the red and infrared regions are commonly found in optical data storage applications. If laser devices operating at shorter wavelengths such as green, blue/green and blue were available, the data storage density of optical data storage devices could be increased. However, practical semiconductor laser diodes operating at the shorter wavelengths have not as yet been manufactured. The prior art has focussed on a variety of means for utilizing II/VI materials to provide shorter wavelength semiconductor lasers.
Blue-green II/VI semiconductor injection lasers have been produced by Haase, et al. ("Blue-Green Laser Diodes", Appl. Phys. Lett. 59 (11), 9 Sep. 1991) using a separate-confinement heterostructure (SCH) configuration. These lasers have ZnS.sub.0.06 Se.sub.0.94 cladding layers, a ZnSe waveguiding region, and a Cd.sub.0.2 Zn.sub.0.8 Se quantum-well active region. Although this configuration has provided room-temperature pulsed and low-temperature continuous operation, it has the disadvantage that it cannot be grown with all layers pseudomorphic to the GaAs substrate. Pseudomorphic lasers can be made without separate confinement, by omitting the ZnSe guiding region, but additional quantum wells are required to compensate for the reduction in optical confinement. Consequently, the threshold current density increases. Also, the improvement in optical confinement obtained by additional quantum wells is limited, because the large lattice mismatch (about 1.5%) between Cd.sub.0.2 Zn.sub.0.8 and ZnS.sub.0.06 Se.sub.0.94 limits the total thickness of Cd.sub.0.2 Zn.sub.0.8 Se. Growth of Zn.sub.1-x Mg.sub.x S.sub.y Se.sub.1-y materials by MBE has been demonstrated by Okuyama, et al (Jap. J. App. Phys. 30, L1620 (1991)). They have implemented Zn.sub.1-x Mg.sub.x S.sub.y Se.sub.1-y cladding layers in optically pumped lasers operating at temperatures up to 500K and in 77K multi-quantum-well p-n injection lasers without separate confinement. The use of Zn.sub.1-x Mg.sub.x S.sub.y Se.sub.1-y for II/VI lasers is also shown in U.S. Pat. No. 5,260,958.
In the past, II/VI (typically ZnSe) semiconductor gain-guided injection laser structures have been fabricated using polyimide or nitride/oxide to define the stripe-geometry lateral current confinement region in these laser structures. However, these materials typically have several disadvantages. Polyimide, for example, requires the use of high curing temperatures that are not compatible with II/VI laser materials and is susceptible to the formation of pinholes. Such pinholes can create undesired alternative conduction paths through the laser device, and thereby degrade device performance. Nitride and oxide have adhesion problems and may also detrimentally heat the laser structure during deposition. Furthermore, neither of these techniques will enhance device efficiency by reducing the effect of lateral current spreading during laser operation.